1. Field of the Invention
The present invention relates to a quinoxaline derivative, and further relates to a light-emitting element, a light-emitting device, and an electronic device using the quinoxaline derivative.
2. Description of the Related Art
An organic compound can take various structures compared with an inorganic compound, and it is possible to synthesize materials having a variety of functions by appropriate molecular-design of an organic compound. Owing to these advantages, photo electronics and electronics which use a functional organic material have been attracting attention in recent years.
For example, a solar cell, a light-emitting element, an organic transistor, and the like are exemplified as electronic devices utilizing an organic compound as a functional material. These are devices taking advantage of electric properties and optical properties of the organic compound. Among them, in particular, a light-emitting element has been making remarkable development.
It is recognized that the light emission mechanism of a light-emitting element is as follows: when voltage is applied between a pair of electrodes which sandwich a light-emitting layer, electrons injected from a cathode and holes injected from an anode are recombined in the light-emitting layer to form a molecular exciton, and energy is released to emit light when the molecular exciton relaxes to the ground state. A singlet excited state and a triplet excited state are known as excited states, and light emission is considered to be possible through any of the excitation states.
In improving element characteristics of such a light-emitting element, there are a lot of problems depending on a material, and in order to solve the problems, improvement of an element structure, development of a material, and the like have been carried out.
For example, tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) is widely used as an electron transporting material of the light-emitting element (see Non-Patent Document 1: Taishi Tsuji, et al., SID 04 DIGEST, 35, PP900-903 (2004)). However, development of materials having more excellent characteristics such as high mobility is desired. In particular, in view of commercialization, less power consumption is an important object, and development of a material and a light-emitting element having further improved characteristics have been desired.